1. Field of the Invention
The present invention generally relates to a centrifugal basket assembly and certain material-drying and screen-protecting methods enabled thereby. More particularly, the present invention relates to a centrifugal basket assembly with segmented dam feature for retarding and/or preventing separator screen wear and tear.
2. Discussion of Prior Art
Centrifugal drying assemblies are well developed and known in a number of relevant arts. With regard to centrifugal dryers for drying solid materials such as coal and the like, the centrifugal drying assemblies are more specifically tailored to meet the demands of the matter to be dried. U.S. Pat. No. 4,922,625 ('625 patent), which issued to Farmer, for example, discloses a Sectionalized Centrifugal Drying Basket/Screen Assembly, which assembly is specifically constructed to minimize wear.
In this last regard, the '625 patent describes a sectionalized screen/basket assembly for a centrifugal dryer for coal slurry comprising a screen formed in an upper section and a lower section, enabling one to save substantially on screen replacement costs, inasmuch as the great preponderance of screen wear in such dryers is at the top of the screen, at the point of slurry introduction. An internal circumferential ridge on the upper screen creates a particle cake that further reduces wear.
Further, U.S. Pat. No. 4,961,722 ('722 patent), which issued to Taylor et al., discloses a Conical Screen for a Vertical Centrifugal Separator. The '722 patent describes an improved vertical centrifugal separator of the type used to dry coal, which improvement is provided by splitting a frustoconical screen into two pieces and including access doors in the water shield surrounding the screen. The division of the screen is made horizontally, for example at a level of about 30 to 70 percent down from the top of the screen.
This permits the separator to be serviced in a relatively short time, by replacing only the upper partial screen when-holes are worn in it. This is feasible because most of the wear in these screens is confined to about the upper 30 percent of their height. If a screen support basket is used, it can be confine to the lower partial screen, so that it does not have to be removed in order to replace the upper partial screen.
It will thus be seen from a review of the '625 patent and '722 patents that centrifugal dryers used for drying coal slurry are subject to wear and tear. The present invention addresses this common adverse side effect in centrifugal dryers by implementing a damming feature at the discharge end of the centrifugal drying assembly. Some of the more pertinent art relating to, or bearing on centrifugal dryer assemblies arguably incorporating a damming or dam-like feature are briefly described hereinafter.
U.S. Pat. No. 3,390,777 ('777 patent), which issued to Grieselhumber, discloses a Feed-Straining Continuous Basket with Trash Trapping Means. The '777 patent describes a centrifugal filter basket having a feed accelerating cup at the bottom thereof for receiving the feed and a trash trapping ring attached to the cup to remove trash from feed passing from the cup to the filter. Arguably, the trash trapping ring could be analogized to resemble a dam type flange.
U.S. Pat. No. 3,946,940 ('940 patent), which issued to Tadokoro, discloses a Centrifugal Basket. The '940 patent describes a basket for a centrifugal separator which has a rotatable shell having at least one flange formed at one end thereof for containing liquid, an exchangeable flat ring having a number of holes radially formed therethrough with respect to the center axis of said shell and removably mounted to the flange of said shell for discharging liquid contained in said shell, and a plurality of circular cover for coating one end surface of said exchangeable ring. Since the basket is thus constructed, it is adapted for high speed rotation.
U.S. Pat. No. 5,458,776 ('776 patent), which issued to Preisser et al., discloses a Sand Dewatering Centrifuge. The '776 patent describes a centrifuge for dewatering a fluent aggregate material such as sand. Sand slurry is conducted into a rotating cylindrical drum which has a perforated lateral wall against which a screen is placed. The drum is oriented with the axis disposed vertically. When the centrifuge operates, centrifugal action slings slurry poured into the drum outwardly. Upon contacting the lateral wall, the slurry builds up. When a certain quantity of the slurry has built up at the bottom or floor of the cylinder, additional material cannot resist migrating upwardly.
Thickness of the trapped layer varies, being greater at the floor, near the source of the incoming slurry. This trapped layer forms a bed having an inclined wall. Thickness of the bed at the top of the cylinder is determined by a circumferential, inwardly projecting flange or dam located at the top of the cylindrical drum. The sand bed protects metal parts of the centrifuge from abrasion, and also enables water to diffuse therethrough. Water is discharged through perforations in the lateral wall, and dewatered sand continues to migrate upwardly. At the top of the drum, this sand migrates beyond the flange, and is slung outwardly against a shroud, which directs the sand to an outer conveyor or chute therebelow. This shroud includes an internal shelf which traps a layer of sand protecting the shroud from erosion by sand ejected from the drum. Water is trapped by a second shroud, and is collected at a suitable discharge chute or conduit.
U.S. Pat. No. 6,244,446 ('446 patent), which issued to Schmittal, discloses a Method and Apparatus for Continuously Separating a More Dense Fraction from a Less Dense Fraction of a Pulp Material. The '446 patent describes a method and centrifugal separator apparatus for separating more dense particles from less dense particles contained in a slurry. The separator apparatus receives slurry into a rotor assembly which includes a bowl open upwardly and a surrounding hutch chamber. The bowl has a lower impermeable portion coupled to a drive shaft for rotating the rotor assembly, an upper impermeable portion connected to the lower portion, and a frusto-conical screen.
The frusto-conical screen forms the inner wall of the hutch chamber and discharge outlets are provided in the periphery of the hutch chamber. An annular fluid inlet connected to the hutch chamber supplies elutriation liquid continuously to the interior of the hutch chamber, and a plurality of pulse blocks supply intermittent pulses of liquid to the hutch chamber. A dam is formed at the top of the screen. In operation, slurry is supplied to the lower portion of the bowl and forms a bed on the screen.
A continuous flow of liquid is supplied axially inwardly from the hutch chamber through the screen and slurry bed. Liquid is also lightly pulsed from the hutch chamber axially inwardly through the screen and slurry bed. Under centrifugal, gravitational and liquid flow forces the denser particles migrate toward and through the screen and lighter particles migrate inwardly toward the axis of rotation. The denser particles pass through the screen into the hutch chamber and are collected on exiting from the discharge outlets. The lighter particles are carried over the dam and are collected separately.
U.S. Pat. No. 7,140,494 ('494 patent) and United States Patent Application Publication No. 2006/0151377, which were authored by Fujimoto et al., disclose certain Centrifugal Machines comprising a screen bowl type centrifugal separator which can not only eliminate the problem of the productivity being lowered resulting from the occurrence of clogging with the crystals in the screen part, but also minimize the amount of leakage of the object to be treated in the screen part.
Inside of the hub of the screw conveyor, a cleaning liquid receiving part which receives the cleaning liquid for the cleaning nozzle is provided, and further, in the cleaning liquid receiving part, a residual layer crystal cleaning liquid receiving part which receives the cleaning liquid for cleaning the residual layer object to be treated in the screen part is provided, being partitioned independently of the inside of the cleaning liquid receiving part.
The cleaning liquid which has been supplied to the inside of the residual layer crystal cleaning liquid receiving part is jet spouted directly toward the residual layer object to be treated from the outer circumferential edge of the flight through the residual layer crystal cleaning liquid path provided along the direction of the helix of the flight, with no relation to said cleaning liquid receiving part.
U.S. Pat. No. 7,425,264 ('264 patent), which issued to Reig, discloses a Centrifugal Screen. The '264 patent describes a centrifuge which has a truncated-cone-like separating screen arranged in support basket and held in the bottom thereof by lower flange. The lower flange has notched surface which penetrates into the screen. The screen and the basket both have an annular upper edge and an upper flange which is attached to the upper edge of the basket and covers the upper edge of the screen. Finally, the screen is formed by a number of segments attached in pairs by a joint with a T-shaped section.
From a review of the above-referenced patents and other prior art generally known to exist that the prior art does not teach a damming feature for a centrifugal basket assembly, which damming feature comprises an annular ring of separate dam segments or dam hooks outfitted upon the rim of the separator screen. A plurality of side-by-side dam segments arranged annularly about the rim periphery of the screen rim and arranged so as to eliminate gaps therebetween is unknown heretofore in the pertinent art. The prior art thus perceives a need for such an arrangement, as described in more detail hereinafter.